The present invention relates in general to headlamp assemblies for motor vehicles, and, more specifically, to housing structures for passively increasing air circulation.
Headlamp assemblies for motor vehicles typically include a housing and a lens cover creating a chamber that contains a light source, such as an incandescent lamp, a light emitting diode (LED), a high intensity discharge (HID) lamp, or a projection lamp, electrically connected to a power source. The chamber may also include a reflector surrounding the light source or the housing itself may be made reflective.
During operation of the light source (i.e., during illumination driven by the power source), heat is generated within the chamber which must be removed. In some designs, the chamber is hermetically sealed, while in other designs a vent is introduced in the housing. When a vent is used, a membrane or filter is typically required to remove contaminants and to reduce entry of moisture into the chamber which could cause condensation. Thermal management and condensation management are important design aspects for both sealed and vented lamps.
It is desirable to keep light sources cool during use and to maintain relatively constant temperature distribution throughout the chamber. Condensation is related to the partial pressure of water vapor in the air contained in the lamp. As the air is heated, the partial pressure of the water vapor increases. When the high pressure water vapor reaches a cold region, it expands and condensation occurs. In order to avoid hot or cold spots in the chamber, fans have sometimes been added to headlamp assemblies in order to circulate air within the chamber or within a passageway separated from the chamber by a wall. The fan results in added cost and reduced reliability of a headlamp system. Without a fan, however, circulation in conventional headlamp assemblies has been due only to density differences between hot and cold air. Insufficient mixing in conventional assemblies can increase condensation and prevent efficient heat removal from the headlamp.